Static means for generating inertia compensation signals in reel drives

ABSTRACT

Static circuit means is provided for generating an inertia compensation signal in response to a first input signal proportional to the diameter of strip material on a reel and a second signal proportional to the linear acceleration, or deceleration, of the strip material. The inertia compensation signal is utilized in the control for the reel drive motor to maintain strip tension substantially independent of changes in line velocity of the strip.

iiiiitedi Nedreslii tent 1 i 1 STATIC MEANS IFOFR GENERATING llNElR'llA COMPENSATKON SIGNALS 1N REEL DRKVIES {52] US. Cl. 242/7551, 318/6 [51] Int. Cl B65111 25/28 [58] Field 011 Search 242/755, 75.51,

Pell 242/7551 Haley 242/755 Primary Examiner--George F. Mautz Assistant Examiner-Edward J. McCarthy Attorney-James C. Davis, Jr. et al.

[57] ABSTRACT Static circuit means is provided for generating an inertia compensation signal in response to a first input signal proportional to the diameter of strip material on a reel and a second signal proportional to the linear acceleration, or deceleration, of the strip material. The inertia compensation signal is utilized in the control for the reel drive motor to maintain strip tension substanl l Refiel'emes Cited tially independent of changes in line velocity of the UNITED STATES PATENTS strip.

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I s I i ng I I \04 10 I )02 70 i o v- I 8 l l i i 1 |1+ I INVENTOR.

ROBERT 3'. NEDRESKI F'IQZ H ATFORN EY STATIC MEANS FOR GENERATING INERTIA COMPENSATION SIGNALS IN REEL DRIVES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to tension control in strip material handling systems in which strip material is wound upon a reel driven by a variable speed motor and, more particularly, to improved static means for generating an inertia compensation signal related in a predetermined manner to strip acceleration, reel diameter, and the physical characteristics of the material handling system.

2. Description of the Prior Art In the processing of certain sheet materials, such as sheet steel, the material is commonly handled and worked in strip form. It is often desirable that the material be coiled on a reel driven by a variable speed motor, typically a d-c motor. For uniformity of quality of the strip material, it is essential that the tension under which the strip material is wound onto and off of the reel be precisely controlled. In particular, it is essential that changes in the line speed of the strip material not result in rapid or substantial changes in the tension applied by the reel on the strip. It has heretofore been widely recognized in the field that inertia compensation is required during periods of acceleration and deceleration of the strip material to compensate for the inertia of the'moving reel and drive members. Thus, the winding reel motor during periods of acceleration must supply additional torque to bring the moving parts up to the new speed while maintaining the proper tension of the strip material. Conversely, during periods of deceleration, the winding reel motor must supply less torque, which when added to the torque supplied by the inertia of the moving parts trying to maintain their higher speed, will provide the proper tension in the strip material.

It has heretofore been known that the amount of inertia compensation required in a given reel drive during periods of acceleration and deceleration is related to the amount of strip material on the reel, the linear acceleration or deceleration of the strip, and certain fixed physical characteristics of the system. More particularly, it has been known, in theory, that the optimum amount of inertia compensation, I, is related to these factors as follows:

where A represents actual acceleration or deceleration of the strip, D represents the diameter of the strip material on the reel, and K K and K are constants which are fixed for any particular reel drive. Efforts have been made to sense acceleration and coil diameter and to generate an inertia compensation signal in response thereto. These prior art approaches, using motor driven potentiometers and the like, have typically produced compensation signals which are only approximately related to the theoretically desired signals.

SUMMARY OF THE INVENTION It is therefore an object of this invention to generate an inertia compensation signal substantially identical to the theoretically desired signal.

Another object of this invention is to provide static means for generating inertia compensation signals for use in reel drives for strip material handling systems.

Yet another object is to provide improved static means for enabling the maintenance of strip tension by a reel drive during linear acceleration and deceleration of strip material.

A still further object of this invention is to provide the foregoing objects by static means of relatively simple and uncomplicated form.

Briefly stated, in carrying out the invention in one form, an improved inertia compensation signal generating means is provided for a strip material handling system including a reel upon which strip material is wound under controlled tension, a variable speed motor, and motor control means responsive to control signals including the inertia compensation signal. The inertia compensation signal generating means is effective during strip acceleration and deceleration to produce a signal having a magnitude such that tension variations due to acceleration and deceleration are substantially prevented. The signal generating means of this invention includes means for generating a diameter signal proportional to the diameter of the strip material coiled on the reel, means for generating an acceleration signal proportional to the rate of change of linear velocity of the strip material,.and static circuit means responsive to the diameter signal and the acceleration signal to generate the inertia compensation signal. By a further aspect of the invention, the static circuit means is comprised of a plurality of solid state devices interconnected to operate on the diameter and acceleration signals such that the magnitude of the inertia compensation signal is established by:

where I is the magnitude of the inertia compensation signal, A is the magnitude of the acceleration signal, D is the magnitude of the diameter signal, and K K and K are constants of proportionality.

BRIEF DESCRIPTION OF THE DRAWINGS system having a reel drive in which tension is precisely regulated in accordance with this invention; and

FIG. 2 is a circuit diagram of the static inertia compensation signal generation apparatus of this invention.

DETAILED DESCRIPTION Referring now to FIG. I, a strip handling system, such as might be utilized for handling sheet steel and the like, is illustrated in a simplified diagrammatic form. The sheet material, indicated generally by the numeral 10, has a linear velocity determined by the rate of rotation of work rolls l2 and 14 which are driven by a variable speed d-c motor 116. The speed of the motor 16 and, consequently, the linear speed of the strip 10 is regulated by control apparatus 18 in accordance with a reference signal REF-ll supplied to the control apparatus and a speed feedback signal from a tachometer 20 driven by the motor 116. As is wellknown in the art, the control apparatus 13 operates in response to the reference signal REF-l and the feedback signal from the tachometer 20 to control the rate at which electric power from an a-c source is transformed to d-c power by power conversion apparatus 22 and supplied to the armature and field windings 24 of the motor 16.

The strip of sheet material is, depending upon the direction in which the strip lltl is driven by the rolls l2 and 14, either wound onto or off of a reel 30, which is driven by a variable speed d-c motor 32. It is extremely desirable that the reel 30 be driven such that variations in the line speed of the strip 10 do not result in corre sponding variations in strip tension. Stated differently, it is desirable that the reel 30 be driven by the motor 32 such that the tension in the strip 10 is precisely determined by the magnitude of a reference signal REF-2 supplied to control apparatus 34. In some strip handling applications, this reference signal REF-2 may be maintained at a constant level so that the strip 10 is coiled onto the reel at a uniform tension. Alternatively, it may be desirable to vary the magnitude of the reference signal REF-2 so that the tension will vary in a predetermined manner. For example, taper tension reeling is' often practiced, this approach providing a gradually reduced tension as the strip material builds up on the reel 30. In any event, it is desirable that a change in line speed not result in an abrupt change in strip tension.

Let it now be assumed that the motor 32 is being operated in the constant horsepower range under substantially steady state conditions (the line speed of the strip 10 is substantially constant). Let it also be assumed that windage and friction losses are low relative to the torque providing the strip tension. Under these conditions, the armature current supplied to the motor 32 is directly proportional to motor torque and strip tension. By utilizing a current feedback signal derived from the voltage drop across a resistor 36 in the armature circuit, the armature current and therefore the tension of the strip 10 can be regulated by the reference signal REF-2. When the actual current, and therefore strip tension, is equal to that called for by the reference signal REF-2, the feedback signal on line 38 to the control apparatus 34 will be equal to the reference signal REF- 2, and the power conversion apparatus 40 will continue to transfer electric power from an a-c source to the armature and field 42 of the motor 32 at a rate sufficient to maintain the scheduled tension. If, however, the actual tension should increase, the negative feedback signal on line 38 will similarly increase, and the control apparatus 34 will respond by reducing the armature current supplied by the power conversion apparatus 40 so as to thereby reduce the actual tension. Similarly, if the actual tension should decrease, the negative feedback signal will decrease and the control apparatus 34 will respond by increasing the armature current so as to increase the actual tension to that called for by the reference signal REF-2.

As pointed out above, inertia compensation is required during periods of strip acceleration or deceleration if the strip tension is to be regulated in accordance with reference signal REF-2. More particularly, the motor 32 must supply additional torque (and armature current) during periods of acceleration and less torque (and armature current) during periods of deceleration. To accomplish this, there is provided in accordance with this invention a solid state circuit or network 44 which is supplied on line 46 with a signal directly proportional to the rate at which the linear velocity of the strip 10 is changing and which is supplied on line 48 with a signal directly proportional to the actual diameter of the roll of strip material on the reel 30. The incrtia compensation network 44 includes, in accordance with this invention, solid state multiplying and dividing devices which operate on the input signals on lines 46 and 48 to produce on output line 50 an inertia compensation signal. The elements comprising the inertia compensation circuit 44 are selected such that the inertia compensation signal on line 50 will, when combined with the REF-2 signal and the negative current feedback signal on line 38, provide a net signal to the control apparatus 34 having a magnitude sufficient to accurately maintain the tension called for by the reference signal REF-2 during strip acceleration and deceleration.

Still referring to FIG. 1, a lever 56 having a roller 58 on one end thereof is provided, the roller 58 riding on the outer surface of the coil of strip material on the reel 30 so that the position of the lever 56 provides a mechanical indication of the diameter of the strip material on the reel 30. Suitable electrical means, such as a potentiometer, is provided within block 60 to convert the position of the lever 56 into an electrical signal directly proportional to the diameter of the coil 'of strip material. The electrical signal generated by the electrical apparatus of block 60 is supplied over line 48 to the inertia compensation network 44. The exact nature of the apparatus utilized to generate the diameter signal is, of course, not significant with respect to this invention since the signal can be generated in many ways. For example, the electromechanical approach just described could be replaced by an optical arrangement in which the diameter of the coil is sensed optically by photoelectric cells or the like. Other approaches for generating a diameter signal directly proportional to the coil diameter will readily occur to those skilled in the art. Similarly, various approaches may be utilized to generate the acceleration signal supplied over line 46 to the inertia compensation network 44. One suitable approach is illustrated by FIG. 1. As shown, the control apparatus 18 for the motor 16 includes apparatus 62 for converting a step change in the magnitude of the reference signal REF-1 from a first level to a second level into an output signal REF-3 which changes gradually from the first level to the second level over a period of time. As a result of this gradual change in the magnitude of the signal REF-3, the strip 10 will not be subjected to an abrupt change in its speed, but will be gradually accelerated or decelerated by the rolls l2 and 14 to the proper speed. At this point, it will be appreciated that the acceleration or deceleration of the strip 10 is proportional to the rate at which the magnitude of the signal REF-3 is changing. Since devices such as 62 are widely used in strip handling systems to insure smooth changes in line speed, it is convenient to obtain from such a device an electrical signal indicative of the rate at which the line speed is changing. As in the case of the diameter signal, however, other approaches can be utilized for generating the acceleration signal supplied to the inertia compensation network 44.

Referring now to FIG. 2, the novel and completely static inertia compensation circuit or network 44 will be described. The circuit 44 includes, as shown, two solid state multiplying elements 66 and 68 and a solid state dividing element 70. In actuality, the elements 66, 68 and 70 are structurally identical, the arithmetic function of each element being determined by the manner in which it is wired into the circuit. Solid state multiplying and dividing elements of the type illustrated are well-known to those skilled in the art and are commercially available. In one embodiment of the present invention, the elements 66, 68 and 76 were obtained from Motorola Semiconductor Products, inc. and were identified by the manufacturer as Model No. MCl595L.

As pointed out previously, the function of the circuit 44 is to receive the variable acceleration and diameter signals on lines 46 and 48, respectively, and to generate in response thereto an inertia compensation signal on line 58. Furthermore, the inertia compensation network operates on the input signals such that the resulting inertia compensation signal is related to the accel eration and diameter signals in accordance with l.== 1K,A (D K (K A/D where l is the magnitude of the inertia compensation signal on line 58, A is the magnitude of the acceleration signal on line 46, and D is the magnitude of the diameter signal on line 48. K,, K and K are constants which are fixed in accordance with the physical characteristics of the reel drive and the strip material such that the resulting magnitude ofl will be that required, throughout the entire ranges of A and D, to compensate for inerta characteristics of the reel drive and thereby maintain the tension prescribed by the reference signal REF-2. More particularly, the magnitudes of the constants l(,, K, and K are selected such that K A (D K provides compensation for inertia changes related to the amount of strip material on the reel and MA) provides compensation for the fixed inertia of the strip handling apparatus.

The inertia compensation circuit 44 will now be described with reference to FIG. 2. The line 48 is connected to the multiplying element 66 at multiplier inputs 72 and 74 such that the element 66 multiplies the magnitude of the diameter signal by itself to produce at product output 76 a signal having a magnitude equal to the square of the magnitude of the diameter signal. In terms of the foregoing equation, the signal produced at output 76 of element 66 is D. By line 78, the signal D is supplied to a differential multiplier input 88 of multiplying element 68. An adjustable potentiometer 82 interconnected betweena source 84 of positive potential and a common point 86 of zero potential is provided, and the wiper arm .88 is adjusted such that a fixed signal is supplied to differential input 90 of the multiplying element 68. For a given reel drive, the potentiometer 82 is adjusted so that the fixed signal supplied to input 90 is equal to the signal D supplied to input 86 when the reel is empty. Furthermore, the differential inputs 80 and 90 are selected such that the magnitude of the signal supplied to input 88 is subtracted from the magnitude of the signal supplied to input 80, the difference being multiplied by element 68 by the magnitude of a signal supplied to input 82. In terms of the foregoing equation, the difference between the signals at inputs 80 and 98 is D K A potentiometer 94 is interconnected between line 46 and the common point 86 with the wiper arm 96 of the potentiometer adjusted such that the acceleration 6 signal A on line 46 is mutliplied by a constant K the product l(,A being-supplied over line 98 to the input 92 of multiplying element 68. It will now be appreciated that element 68 operates on its input signals to produce at its output 168 a signal having a magnitude l(,A (D" K in terms of the above equation. It will also be appreciated that the signal at output 1108 is related to the inertia changes associated with the amount of strip material on the reel when it is noted that the signal will be zero when there is no strip material on the reel, i.e., when D K Furthermore, under conditions of zero acceleration or deceleration, the signal A on line 46 will have zero magnitude, and this will cause the output signal at 1180 to be zero no matter how much strip material is on the reel.

A potentiometer 1102 is interconnected between line 416 and the common point 86 with the wiper arm 1104 of the potentiometer 102 adjusted such that the acceleration signal A on line 46 is mutliplied by a constant K the product K A being supplied over line 1106 to the dividend input 188 of dividing element 70. The divisor input 118 of element is connected by line 112 to the output 76 of element 66 to receive therefrom the signal D The element 70 operates on the signals supplied to its inputs 108 and l 10 to produce at output 1 M a signal having a magnitude li( -,A/D in terms of the above equation. The signals K,A (D K and li A/D from outputs 188 and 114 of elements 68 and '78, respectively, are supplied to a summing junction 116 from which the combined signal is supplied on line 58 to control apparatus 34L From the foregoing, it will be seen that this invention provides completely static means for providing an inertia compensation signal substantially identical to the theoretically desired compensation signal for a particular reel drive system. Although adjustable potentiometers 82, 94 and R02 are shown, it will be appreciated that no adjustments are made during actual operation of the strip material handling system, the illustrated adjustable potentiometers being provided so that a single circuit 44 may be utilized in conjunction with a broad range of reel drive applications.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form, details, and application may be made therein without departing from the spirit and scope of the invention. For example, the elements comprising the inertia compensation circuit 44 can take on forms differing from those illustrated and can be combined in various ways to provide the static arithmetic operations described herein; Furthermore, although the invention has been illustrated in d-c reel drive system, it is equally applicable to a-c drive systerns. Accordingly, it is intended that all such modifications and changes be included within the scope of the appended claims.

What is claimed as new and is desired to secure by Letters Patent of the United States is:

ll. In strip material handling apparatus including a reel upon which the strip material may be wound and unwound under controlled tension, variable speed motor drive means'for driving'the reel, and motor control means responsive to control signals including an inertia compensation signal effective during acceleration and deceleration of the strip material, inertia compensation signal generating means comprising:

means for generating a diameter signal directly proportional to the diameter of the strip material wound on the reel,

means for generating an acceleration signal directly proportional to the rate of change oflinear velocity of the strip material,

and static circuit means, including a plurality of static circuit elements, coupled to said diameter signal generating means and said acceleration signal generating means for receiving said diameter and acceleration signals therefrom, said static circuit means being responsive to said diameter and acceleration signals to generate an inertia compensation signal having a magnitude established by:

where I is the magnitude of the inertia compensation signal, A is the magnitude of the acceleration signal, D is the magnitude of the diameter signal, and K K and K are constants established in accordance with physical and operational characteristics of the strip material handling apparatus and the strip material being handied.

2. Inertia compensation signal generating means as defined by claim 1 wherein K D when the reel has no strip material wound thereon.

3. lnertia compensation signal generating means as defined by claim 4 wherein said circuit elements include solid state devices for performing arithmetic operations on the diameter and acceleration signals.

4. Inertia compensation signal generating means as defined by claim 5 wherein the magnitudes of K,, K and K are selected such that:

K A(D K provides compensation for inertia changes related to the amount of strip material on the reel, and,

K A/D provides compensation for the fixed inertia of the strip handling apparatus.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,762,663

DATED October 2, 1973 INV ENTOR(S) Robert Joseph Nedreski It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 7, delete "4" and substitute -2.

Column 8, line 11, delete "5" and substitute --3---.

Signed and Sealed this tenth D ay 0f February 1976 .[SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofPatenrs and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 2 3,762,663

DATED I October 2, 1973 INVENTOR(S) Robert Joseph Nedreski It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 7, delete "4" and substitute -2.

Column 8, line ll, delete "5" and substitute -3-.

Signed and Scaled this tenth Day Of February 1976 [SEAL] A nest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (ummissr'nner uj'Parents and Trademarks 

1. In strip material handling apparatus including a reel upon which the strip material may be wound and unwound under controlled tension, variable speed motor drive means for driving the reel, and motor control means responsive to control signals including an inertia compensation signal effective during acceleration and deceleration of the strip material, inertia compensation signal generating means comprising: means for generating a diameter signal directly proportional to the diameter of the strip material wound on the reel, means for generating an acceleration signal directly proportional to the rate of change of linear velocity of the strip material, and static circuit means, including a plurality of static circuit elements, coupled to said diameter signal generating means and said acceleration signal generating means for receiving said diameter and acceleration signals therefrom, said static circuit means being responsive to said diameter and acceleration signals to generate an inertia compensation signal having a magnitude established by: I K1A (D2 - K2) + (K3A/D2) where I is the magnitude of the inertia compensation signal, A is the magnitude of the acceleration signal, D is the magnitude of the diameter signal, and K1, K2 and K3 are constants established in accordance with physical and operational characteristics of the strip material handling apparatus and the strip material being handled.
 2. Inertia compensation signal generating means as defined by claim 1 wherein K2 D2 when the reel has no strip material wound thereon.
 3. Inertia compensation signal generating means as defined by claim 4 wherein said circuit elements include solid state devices for performing arithmetic operations on the diameter and acceleration signals.
 4. Inertia compensation signal generating means as defined by claim 5 wherein the magnitudes of K1, K2 and K3 are selected such that: K1A(D2 - K2) provides compensation for inertia changes related to the amount of strip material on the reel, and, K3A/D2 provides compensation for the fixed inertia of the strip handling apparatus. 